I have brewed a couple of smoked porters in the past few months. I based it loosely on Jamil's recipe in Brewing Classic Styles. I used 3 pounds of smoked malt and found that to be enough to give a good smoke flavor.
It takes about 30 gallons of sap to make a gallon is syrup so 7 gallons in your brew kettle doesn't amount to very much syrup.
They also filter out the silt before bottling.
There was such an off flavor from what I could tell was due to the mineral rich sap.
If you live near any sugar...
I rinse my bottles out and run them through the dishwasher and store them upside down.
When I am ready to bottle, I put the already cleaned bottles back in the dishwasher with a tablespoon of the no rinse sanitizer powder.
Then I open up the dishwasher and bottle right there, if any spills, it...
I had the bright idea to replace my brewing water with maple sap once......bad idea.
I also brewed with maple syrup and found that it dried out during fermentation almost completely.
I haven't been brave enough to try it in another beer since.